I worked on this myself and finally decided to try wireless HDMI. I purchased a transmitter and 3 receivers. Now I have HD at all 4 TVs. The system is a little pricey, but it works pretty well. (sometimes you have to reset it when you first start camping)

Actiontec My Wireless TV

If you want to stay with the same type of A/V switch Amazon has the Allnice 4 way AV switch for $12 or less.